1. Technical Field
This disclosure generally relates to binary polarization modulators and, more specifically, relates to the application of binary polarization modulators to time sequential stereoscopic projection systems.
2. Background
Time sequential stereoscopic projection systems alternately present full-frame left and right perspective imagery to the appropriate eye. As such, they use the synchronous operation of a projector with some form of shuttering mechanism. Among the benefits, this approach enables single-projector 3D display, which automatically provides accurate registration of the two images. The elements of the shuttering system may not all reside at the viewer, but some form of analyzer should be used at the viewer to discriminate between the encoded images. In polarization based systems, the simplest approach places orthogonal polarization analyzers at the viewer, with the other elements of the shutter residing at the projector. Typically, the latter includes an input polarizer, and some form of active polarization switch. This has the benefit of minimizing the cost and complexity, since only a single copy is used for elements upstream of the analyzer. However, it places stringent demands on the polarization dependence of any additional elements placed within the shutter (e.g. the screen).
An exemplary display technology is capable of delivering very fast switching (e.g., <100 μs), such that there is complete temporal separation of images. In many instances, there is a further preference for auxiliary shuttering that accommodates the finite switching time of the 3D shuttering means, thereby reducing cross-talk (partial transmission of the wrong image). Such is the case with digital light processing (DLP) projection systems, which for instance, allow liquid crystal (LC) polarization switching transitions to be hidden by high-speed, high dynamic range, shuttering of the display. In principle, the encoding means may be any technology that makes it possible to deliver the appropriate image to each eye. This can include any pair of non-overlapping spectra, any set of orthogonal polarizations, and even angle or position. At present, polarization based systems are most common in the digital cinema.
The most common polarization switches utilize high-speed LC modes. While such devices are used in a high percentage of 3D digital cinema platforms, they do have some performance deficiencies. In particular, high contrast is difficult to maintain for systems operating at low throw-ratios (such as those in home/office environments). Also, LC device operation is most convenient with circular polarization, but there are instances where linear polarizers are preferred (e.g. markets with extreme eyewear price sensitivity, or situations where linear polarizer eyewear is already prevalent, such as theme parks). In addition, current systems typically suffer some on-state efficiency loss due to the chromatic nature of the retarder films used in circular polarization based systems.